Calculating live online TV latency to avoid social media spoilers

Live sports and online video latency aren’t the best of friends. If you’re watching a live game using an online service and your feed is lagging behind the traditional broadcast feed, then spoilers are a real problem. Your experience can be ruined by a neighbour cheering through the wall or by a text message from a friend. But the most common culprit for latency spoilers is social media.

A recent poll from Nielsen found that more than 84 per cent of US tablet and smartphone owners use their devices while watching TV. A huge number of sports fans watch games with an eye on social media – namely Twitter – for real-time reactions to the action.

Delays to an online stream can come from within the origin system, the distribution network or within the client itself. The question we’ve had from several people is how low does latency need to be before social media spoilers aren’t a problem? Essentially - how can your feed beat a tweet?

The science bitSo we decided to take it upon ourselves to work it out. If the average time it takes for someone to create, send and react to a social media post is greater than the delay of the TV delivery system, then we don’t have a problem.

Or, put formulaically:

Ts must be ≥ (Lo + LCDN + Lc )

In this formula:

Ts refers to the Time it takes to create, send and react to a social media postLo is the segmentation delay in the originLCDN is the latency across a purpose-built TV CDN system andLc is the latency introduced by a client buffering typical video segments.

If we assume the segment length is three seconds and the client is buffering three segments at a time, then Lo = three secs and Lc = nine secs. And if the TV CDN is built using Edgeware technology we know LCDN ≤ one second. So what we’re trying to ascertain is whether Ts is less than or equal to 13 seconds.

Calculating the speed of a tweet Ts includes a few different things – the time it takes to react to an event, compose and input the tweet, the latency of Twitter’s service itself and the time taken for the viewer to be disrupted.

Calculating this figure exactly takes us into a field called mental chronometry and fortunately there are a number of existing research areas we are able to turn to in order to answer our question. We do have the nuts and bolts of this but we have worked out that Ts is usually greater or equal to 14.75 seconds.

And of course 14.75 seconds is more than 13. Which means that content distributors can deliver TV over an IP distribution network in less time than it takes to receive a spoiler via social media.

But that is dependent on building a well-designed TV CDN where the latency of the delivery network is less that one second. If a distributor is renting space on general-purpose CDN the delay will often be far more – pushing the overall delay the wrong side of the boundary.

Thankfully Edgeware is able to help, having built over 100 such latency-reducing TV CDNs for its customers around the world. By deploying this kind of delivery network that’s just used for TV services, content distributors can save consumers’ games being spoiled, creating a better overall viewing experience.